1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling downlink control information and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (COMP) transmission/reception, UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The CA is introduced to the LTE-A system by which more than one component carriers (CCs) are aggregated to achieve a wide-band transmission. Accordingly, the LTE-A system can support a wide bandwidth up to 100 MHz by aggregating a maximum number of 5 component carriers, where a maximum bandwidth of each component carrier is 20 MHz and is backward compatible with the 3GPP Rel-8 standard. The LTE-A system supports the CA for both contiguous and non-contiguous component carriers. The CA increases bandwidth flexibility by aggregating the component carriers. When a UE is configured with the CA, the UE has the ability to receive and/or transmit packets on one or multiple component carriers to increase throughput.
When the UE is configured with the CA, the eNB may need to arrange (i.e., schedule) resources in one or more subframes of one or more component carriers to the UE. Thus, the eNB needs to spend a large amount of resources on transmitting downlink (DL) control information (DCI) to the UE, to indicate the arranged resources to the UE. However, capacity of a DL control channel (e.g., physical DL control channel (PDCCH)) is limited, and is sufficient for transmitting the DCI for arranging various resources of the subframes and the component carriers. Thus, methods for transmitting the DCI efficiently and receiving the DCI correctly are needed, and are important topics to be discussed.